Relatives of the victims carry an injured man outside a hospital after a suicide attack in Kabul, Afghanistan. Picture: Reuters/Mohammad Ismail

Kabul, Afghanistan - An Islamic State (Isis) suicide bomber killed at least 48 people including women and children and wounded 112 outside a voter registration centre in the Afghan capital Kabul on Sunday in the latest attack on election preparations.

The assaults underscore growing concerns about security in the lead-up to legislative elections scheduled for October 20, which are seen as a test-run for next year's presidential poll.

"It happened at the entrance gate of the centre. It was a suicide attack," Dawood Amin, Kabul police chief, told AFP.

Both the health and interior ministries confirmed the latest toll for the attack, which was claimed by the Islamic State group via its propaganda arm Amaq.

"They are civilians, including women and children," said interior ministry spokesman Najib Danish.

The centre in a heavily Shiite-populated neighbourhood in the west of the city was also being used by people to register for national identification certificates, which they need to sign up to vote.

Sheets of paper and passport-sized photos lay scattered amid shattered glass and pools of blood on the street near badly damaged cars -- grim evidence of the force of the blast that drew international condemnation.

"This senseless violence shows the cowardice and inhumanity of the enemies of democracy and peace in Afghanistan," US ambassador John Bass wrote on Twitter. NATO also condemned the bombing.

The last major attack in Kabul was on March 21 when an Isis suicide bomber blew himself up in a crowd celebrating the Persian New Year holiday and killed at least 33 people.

- Voter security -

Ariana TV showed angry crowds shouting "Death to the government!" and "Death to the Taliban!"

A wounded man in a hospital bed wept as he told the network: "I don't know where my daughters are. God damn the attackers!"

A witness to the attack named Akbar told Tolo TV: "Now we know the government cannot provide us security: we have to get armed and protect ourselves."

Elsewhere, a roadside explosion in the northern province of Baghlan on Sunday killed six people, including three women and two children.

President Ashraf Ghani condemned both attacks as "heinous".

Afghanistan began registering voters on April 14 for the long-delayed legislative elections.

Officials have acknowledged that security is a major concern because the Taliban and other militant groups control or contest large swathes of the country.

Afghan police and troops have been tasked with protecting polling centres, even as they struggle to get the upper hand against insurgents on the battlefield.

Militants on Friday launched rockets at a voter registration centre in the northwestern province of Badghis.

At least one police officer was killed and another person was wounded, officials said, blaming the Taliban.

On Tuesday gunmen attacked a voter registration centre in the central province of Ghor, kidnapping three election workers and two policemen.

Taliban militants released the five on Thursday.

Over the next two months, authorities hope to register up to 14 million adults at more than 7 000 polling centres for the parliamentary and district council elections.

Officials have been pushing people to register amid fears a low turnout will undermine the credibility of the polls.

Since the Persian New Year attack a tense calm has permeated the Afghan capital as people brace for the Taliban's launch of its customary spring offensive.

The Taliban are under pressure to take up Ghani's peace offer made in February but so far the group has given only a muted response.

Some Western and Afghan officials expect 2018 to be a particularly bloody year.

General John Nicholson, the top US and NATO commander in Afghanistan, told Tolo TV last month that he expected the Taliban to carry out more suicide attacks this fighting season.